Hydration of Bilayered Graphene Oxide Rezania, B; Severin, Nikolai; Talyzin, Alexandr V ...
Nano letters,
07/2014, Volume:
14, Issue:
7
Journal Article
Peer reviewed
The hydration of graphene oxide (GO) membranes is the key to understand their remarkable selectivity in permeation of water molecules and humidity-dependent gas separation. We investigated the ...hydration of single GO layers as a function of humidity using scanning force microscopy, and we determined the single interlayer distance from the step height of a single GO layer on top of one or two GO layers. This interlayer distance grows gradually by approximately 1 Å upon a relative humidity (RH) increase in the range of 2 to ∼80%, and the immersion into liquid water increases the interlayer distance further by another 3 Å. The gradual expansion of the single interlayer distance is in good agreement with the averaged distance measured by X-ray diffraction on multilayered graphite oxides, which is commonly explained with an interstratification model. However, our experimental design excludes effects connected to interstratification. Instead we determine directly if insertion of water into GO occurs strictly by monolayers or the thickness of GO layers changes gradually. We find that hydration with up to 80% RH is a continuous process of incorporation of water molecules into single GO layers, while liquid water inserts as monolayers. The similarity of hydration for our bilayer and previously reported multilayered materials implies GO few and even bilayers to be suitable for selective water transport.
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•We exfoliated graphenes onto mica in ambient with and without adhesive tapes.•Only graphenes exfoliated without the aid of adhesive tapes are mostly flat.•Topography of graphenes ...exfoliated with tape depends on particularly used tape.•Structure of water adlayer visualized with graphene can be controlled by additives.
Molecular adlayers on mica have been visualized previously by coating the sample with graphene and imaging it by scanning force microscopy. While it had been argued that this shows that ambient water on mica exhibits ice-like structures, recent apparently similar experiments indicate different behaviors. Here, we demonstrate that adhesive tapes, which are often used to mechanically exfoliate graphenes onto solid substrates, can lead to water-containing adlayers, which differ substantially from pure water layers. We exfoliated graphenes with the aid of different adhesive tapes and demonstrate that the results depend on the particular tape. Our results imply that structure and properties of confined water adlayers can be controlled by minor amounts of additives.
Hydrogen-dependent denitrification has gained significant attention due to its potential economic advantage over heterotrophic denitrification. However, effective hydrogen delivery and biomass ...retention under anaerobic conditions are significant challenges to implementation of this process. An innovative hydrogenotrophic denitrification system, that addresses these challenges, consisting of an anaerobic submerged membrane bioreactor (MBR) and a novel hydrogen delivery unit, was evaluated for removal of nitrate from a synthetic groundwater feed. The hydrogen delivery unit was designed to release hydrogen-supersaturated water to the reactor and was efficient in hydrogen delivery, providing complete mass transfer. The anaerobic submerged MBR was successful in both reducing nitrate from 25
mg
NO
3–N
l
−1 to below detection and separating biomass from treated water to produce effluent free of suspended solids. Nitrogen gas produced during denitrification was internally recycled to effectively achieve membrane scouring and reactor mixing. The total organic carbon was similar to that of the incoming feed water, averaging approximately 6
mg
l
−1.
This paper presents the operational strategy for nitrogen removal in a two-stage, partial nitrification (PN) process coupled with anaerobic ammonium oxidation (Anammox) process. The process was used ...to remove ammonium from centrate obtained from a full-scale, wastewater treatment plant in British Columbia, Canada. The PN, which was carried out in a sequencing batch reactor (SBR), successfully converted ∼ 49.5±1.0% of ammonium to nitrite. The operation of SBR under higher dissolved oxygen in combination with slow feeding resulted in significant reduced HRT without nitrate accumulation. Partially nitrified centrate was further treated in Anammox reactors, where the mixture of ammonium and nitrite was converted mainly to nitrogen gas. Anammox treatment was carried out in two different types of Anammox reactors: a moving bed hybrid reactor and an up-flow fixed-bed biofilm reactor. The hybrid Anammox reactor removed an average of 55.8% of NH ₄-N, versus the 48.3% NH ₄-N removed in the up-flow fixed-bed reactor. Nitrite removal in the hybrid and up-flow fixed-bed Anammox reactors averaged 80.8% and 62.5%, respectively. This study also illustrated that in both Anammox reactors, better ammonium removal was achieved when the nitrite to ammonium ratio is between 1.35 and 1.45. As such, alkalinity was found to neither control nor limit the Anammox reaction.
A hydrogenotrophic denitrification system, comprising a suspended growth membrane bioreactor (MBR) with membrane hydrogen gas diffusion, was developed to remove nitrate from groundwater. A hollow ...fiber gas permeable membrane module was designed for hydrogen delivery and a commercially available hollow fiber membrane module was used for solid/liquid separation. The MBR was operated at an SRT of 20 days and at room temperature. Four nitrate loading rates of 24, 48, 96 and 192 NO3(-)-N mg I(-1) d(-1) were applied to the system. As the nitrate loading was raised, pH increased due to increased denitrification and release of OH- ions. The oxidation reduction potential (ORP) remained fairly stable when full denitrification was achieved, but increased when nitrate loading rates reached 192 NO3(-)-N mg I(-1) d(-1) and residual nitrate was present in the reactor. Nitrate removal was complete (100%) in the first three nitrate loadings and 72% in the system with 192 NO3(-)-N mg I(-1) d(-1). Nitrate utilization rates of 30.6, 23.4, and 37.7 g NO3(-)-N m(-3) d(-1) were achieved in the first three loadings. Average effluent dissolved organic carbon (DOC) concentration of approximately 8 mg l(-1) was observed in all four nitrate loading regimes, possibly owing to the generation and release of soluble microbial bi-products (SMP).
A novel hydrogenotrophic denitrification system, which consisted of a sequencing batch membrane bioreactor, was evaluated for simultaneous removal of nitrate and soluble microbial products (SMP) from ...a synthetic groundwater feed. A hollow fiber membrane diffuser was used for bubble-less diffusion of hydrogen into the bioreactor under anoxic condition followed by aerobic SMP removal and biomass filtration. During the anoxic period, the nitrate loading of 0.328 kg N m(-3) d(-1) was completely denitrified to below detectable levels. A denitrification rate of 0.8 kg N m(-3) d(-1) was obtained at steady state biomass concentrations of 1,162 mg I(-1). During the aerobic period when biomass filtration was performed, 81% of SMP produced within the anoxic phase was retained by the membrane, 9% was biologically removed, 5% was passed through the membrane and 5% was discharged during the wasting of mixed liquor. The aerobic cycle was instrumental as it allowed for effective biomass filtration via membrane scouring and assisted in further reduction of effluent organic matter.
An anaerobic submerged membrane bioreactor was coupled with a novel hydrogen delivery system for hydrogenotrophic denitrification of municipal final effluent containing nitrate. The biological ...treatment unit and hydrogen delivery unit were proven successful in removing nitrate and delivering hydrogen, respectively. Complete hydrogen transfer resulted in reducing nitrate below detectable levels at a loading of 0.14 kg Nm(-3) d(-1). The produced water met all drinking water guidelines except for color and organic carbon. However, the organic carbon was removed by 72% mostly by membrane rejection. To reduce the organic carbon and color of the effluent, post treatment of the produced water is required.
A general method for measurement of active biomass and decay coefficient and Extracellular polymeric substances (EPS) concentration in steady-state biomass was developed. The model was applied to the ...process of hydrogenotrophic denitrification in order to measure biomass constituents and decay and yield coefficients. It was found that steady-state biomass obtained after operation at 20 day solids retention time (SRT) was composed of 41% active biomass, 25.6% cell debris and 33.4% extracellular polymeric substance. The value of 0.041 d
−1
, and 0.27 mg active biomass per mg NO
3
-N were obtained for decay coefficient and true yield, respectively.
Femoral nerve injury is a rare but devastating complication of direct anterior approach total hip arthroplasty that occurs in about 1% of the cases and could potentially lead to debilitating loss of ...knee extension. In this case report, we present a case of femoral nerve injury following direct anterior approach hip arthroplasty with an inability to extend the affected knee, gait instability, and multiple falls. For this patient, an innovative functional adductor magnus muscle transfer was performed to restore knee extension. At 6 months after surgery, the patient’s knee extension was partly restored, and ambulation was significantly improved.
